table.tablesorter thead tr .header {
    background-image: url(images/bg.gif);
    background-repeat: no-repeat;
    background-position: center right;
    cursor: pointer;
    padding-right: 2em;
}

table.tablesorter thead tr .headerSortUp {
	background-image: url(images/asc.gif);
}
table.tablesorter thead tr .headerSortDown {
	background-image: url(images/desc.gif);
}